:root {
  --primary-color: #3080ff;
  --secondary-color: #64b5f6;
  --highlight-color: #00c4ff;
  --bg-color: #f8f9fa;
  --text-color: #212529;
  --card-bg: #ffffff;
  --card-border: rgba(0, 0, 0, 0.125);
  --section-bg: #f1f3f5;
  --border-radius: 10px;
  --transition-speed: 0.3s;
}

.dark-mode {
  --primary-color: #3080ff;
  --secondary-color: #64b5f6;
  --highlight-color: #00c4ff;
  --bg-color: #121212;
  --text-color: #e0e0e0;
  --card-bg: #1e1e1e;
  --card-border: rgba(255, 255, 255, 0.125);
  --section-bg: #181818;
}

body {
  font-family: 'Roboto', sans-serif;
  color: var(--text-color);
  background-color: var(--bg-color);
  transition: background-color var(--transition-speed), color var(--transition-speed);
  overflow-x: hidden;
}

h1, h2, h3, h4, h5, h6 { font-weight: 700; }

.section-title {
  font-family: 'Orbitron', sans-serif;
  color: var(--primary-color);
  position: relative;
  padding-bottom: 15px;
  margin-bottom: 30px;
}
.section-title::after {
  content: '';
  position: absolute;
  bottom: 0; left: 50%;
  transform: translateX(-50%);
  width: 80px; height: 3px;
  background-color: var(--highlight-color);
}

.highlight { color: var(--highlight-color); font-weight: 700; }
.link-accent { color: var(--highlight-color); text-decoration: none; }
.link-accent:hover { color: var(--primary-color); text-decoration: underline; }

header {
  background-color: var(--bg-color);
  box-shadow: 0 2px 15px rgba(0, 0, 0, 0.1);
  position: sticky; top: 0; z-index: 1000;
  transition: background-color var(--transition-speed);
}
.navbar { padding: 15px 0; }
.brand-name {
  font-family: 'Orbitron', sans-serif;
  font-weight: 700;
  color: var(--primary-color);
  letter-spacing: 1px;
}
.nav-link {
  font-weight: 500;
  margin: 0 5px;
  color: var(--text-color) !important;
  transition: color var(--transition-speed), transform 0.2s;
  position: relative;
}
.nav-link:hover { color: var(--primary-color) !important; transform: translateY(-2px); }
.nav-link::after {
  content: ''; position: absolute; width: 0; height: 2px;
  bottom: 0; left: 50%;
  background-color: var(--primary-color);
  transition: width 0.3s, left 0.3s;
}
.nav-link:hover::after { width: 100%; left: 0; }

.hero-section {
  background: linear-gradient(135deg, var(--section-bg) 0%, var(--bg-color) 100%);
  padding: 100px 0;
  text-align: center;
}
.hero-section h2 {
  color: var(--primary-color);
  font-family: 'Orbitron', sans-serif;
  margin-bottom: 20px;
}
.hero-section p { font-size: 1.15rem; max-width: 780px; margin-left: auto; margin-right: auto; }

.btn-primary {
  background-color: var(--primary-color);
  border-color: var(--primary-color);
  border-radius: var(--border-radius);
  padding: 10px 25px;
  transition: all 0.3s;
}
.btn-primary:hover {
  background-color: var(--highlight-color);
  border-color: var(--highlight-color);
  transform: translateY(-3px);
  box-shadow: 0 5px 15px rgba(0, 0, 0, 0.2);
}

#profile, #projects, #experience, #skills { background-color: var(--bg-color); }
#work, #youtube, #teaching, #contact { background-color: var(--section-bg); }

.card {
  border-radius: var(--border-radius);
  border: 1px solid var(--card-border);
  overflow: hidden;
  background-color: var(--card-bg);
  transition: transform 0.3s, box-shadow 0.3s, background-color var(--transition-speed);
  height: 100%;
}
.card:hover { transform: translateY(-5px); box-shadow: 0 10px 20px rgba(0, 0, 0, 0.15); }
.card-title { color: var(--primary-color); font-weight: 600; }
.card-text { color: var(--text-color); }

.tech-card .card-title { color: var(--highlight-color); }

.about-card {
  background-color: var(--card-bg);
  border-radius: var(--border-radius);
  padding: 25px;
  margin-bottom: 30px;
  border: 1px solid var(--card-border);
  transition: background-color var(--transition-speed);
}
.about-card h4 { color: var(--primary-color); margin-bottom: 15px; }

.commitment-item {
  background-color: var(--section-bg);
  border-radius: var(--border-radius);
  padding: 20px;
  height: 100%;
}
.commitment-item h5 { color: var(--highlight-color); margin-bottom: 10px; }

/* Timeline */
.timeline {
  position: relative;
  padding-left: 30px;
}
.timeline::before {
  content: '';
  position: absolute;
  left: 10px; top: 0; bottom: 0;
  width: 2px;
  background: var(--primary-color);
  opacity: 0.5;
}
.tl-item {
  position: relative;
  margin-bottom: 25px;
  padding: 18px 20px;
  background-color: var(--card-bg);
  border: 1px solid var(--card-border);
  border-radius: var(--border-radius);
}
.tl-item::before {
  content: '';
  position: absolute;
  left: -26px; top: 22px;
  width: 14px; height: 14px;
  border-radius: 50%;
  background: var(--highlight-color);
  box-shadow: 0 0 0 3px var(--bg-color);
}
.tl-date {
  font-family: 'Orbitron', sans-serif;
  font-size: 0.85rem;
  color: var(--highlight-color);
  margin-bottom: 6px;
}
.tl-body h5 { color: var(--primary-color); margin-bottom: 6px; }
.tl-body p { margin-bottom: 0; }

/* Social */
.social-container-sm {
  display: flex; justify-content: center; flex-wrap: wrap;
  gap: 1.3rem; margin-top: 2rem;
}
.social-icon {
  display: flex; align-items: center; justify-content: center;
  width: 3rem; height: 3rem; border-radius: 50%;
  background-color: #000; color: #0d6efd;
  font-size: 1.3rem; text-decoration: none;
  transition: all 0.3s ease;
  box-shadow: 0 2px 5px rgba(0, 0, 0, 0.15);
}
.social-icon:hover { transform: translateY(-3px); box-shadow: 0 5px 15px rgba(0, 0, 0, 0.2); color: var(--highlight-color); }

footer {
  background-color: var(--section-bg);
  color: var(--text-color);
  border-top: 1px solid var(--card-border);
}

@media (max-width: 576px) {
  .hero-section { padding: 60px 0; }
  .social-container-sm { gap: 1rem; }
  .social-icon { width: 2.5rem; height: 2.5rem; font-size: 1.25rem; }
}